The game starts out in the village of Astholm, with you as the head of a 5-person town defense force. The town is spiritually protected by the priestess Phyllis (also your girlfriend), whose power is held to the magical gem, one of seven in the land, she wields. After a succession ceremony, however, she manages to get kidnapped while trysting with you in the rear of town. You and your four-person army head off on a quest to rescue her, but naturally end up getting swept into a much bigger crisis...
The graphics are probably the best you're going to see in a Famicom RPG; there's detail in every part of the game and the character designer (who you might know as the person behind the manga/anime 3X3 Eyes) put great effort into the excellent enemy portraits in battle scenes.
It usually works pretty well, and battles go at a fast clip - however, there are a lot of really annoying limitations. For one, a member of a team will only advance so far ahead of the team's leader - he'll refuse to move after that. Your leader has to do a lot - he decides where the team as a whole goes, and if he's too far from everyone else, you'll have to waste a turn just moving him up.
Because of this, you sometimes have trouble making real formations due to people being in the way, especially in close battles. Let's say there's a wave of fearsome stinging insects coming your way. You want all the straight-out swordsmen at the front, the archers farther back, and maybe any magic users way out in the back to lob fireballs or whatever. In Fire Emblem you're free to move individual units around whenever you want, but here you have to move all your team members individually (unless you're willing to enter auto-mode, which sucks). Since members can't move on top of each other, though, you'll have to waste several turns rearranging everyone the way you want it, with said stinging insects fearsomely stinging everyone and perhaps killing them, which isn't exactly what I would call Team Spirits, huh, Enix?
Another thing that Enix succeeded at that I wouldn't have thought possible is the development of plot along the game. All the characters you have control with over the course of the game have their own personalities, and there are lots of little sub-plots that take advantage of this. Rolan is both the studliest-looking member of your party and the most perverted, and the more even-minded Olof has to protect the women he stalks around with. You find out at one point that Hans hates eating poultry; a fact that comes in handy when your entire party (except him) eats poison-laced chicken and he has to save everyone else's ass.
This is the biggest RPG ever made for the Famicom in physical size - 6 megabits of good graphics and some really incredible music (you'd think there was a sound chip inside the cart, but there isn't). It's currently pretty cheap in the Famicom classic game scene, so if you've got the basics of Japanese down, definitely give Just Breed a try.